Electric-powered power steering apparatus

Abstract

An assist apparatus for electric-powered power steering apparatus is provided to have a torque sensor, steering shaft, preload pad 70, a torsion coil spring 30, and an electric motor 31. With the preload pad 70 and torsion coil spring 30, an elastic force is applied to the worm shaft 29 in the direction toward the worm wheel 28, whereby noises due to colliding teeth are prevented from occurring in the meshing portion between the worm wheel 28 and worm shaft 29.

1 . An assist apparatus for electric-powered power steering apparatus having a torque sensor, assist shaft, worm wheel, worm shaft, elastic force application means and an electric motor,
 comprising first to fourth bearings, and   wherein the torque sensor is located around the steering shaft; the assist shaft is one of the steering shaft, the pinion shaft and a sub-pinion; the worm wheel is fastened around either one of the steering shaft, pinion and sub-pinion; the worm shaft has a worm gear that meshes with the worm wheel; the electric motor comprises a rotating shaft, a rotor that is located on the outer-diameter side of the rotating shaft, and a stator that is located such that it faces the rotor in the radial direction; and the rotating shaft and worm shaft are connected to each other by way of a toothed joint or elastic member,   wherein the first bearing supports inside the casing the end section of the rotating shaft on the opposite side from the worm shaft; the second bearing supports inside the casing the portion of the rotating shaft between the joint, which connects the worm shaft and the rotating shaft, and the rotor; the third bearing supports the end of the worm shaft on the side of the rotating shaft inside the gear housing such that the worm shaft can move free tilt, or move in the axial direction, or free tilt and move in the axial direction, within a specified range; and the fourth bearing supports the end of the worm shaft on the opposite side from the rotating shaft inside the gear housing, wherein a clearance in the radial direction is provided between the inner peripheral surface of the inner race of the fourth bearing and the outer peripheral surface of the worm shaft,   wherein the elastic-force application means comprises an elastic member having a variable spring constant that can be changed from a low spring constant to a high spring constant, and located between the fourth bearing and the worm shaft so as to apply an elastic force to the worm shaft corresponding to the radial displacement of the worm shaft, wherein when not drivers by the electric motor, the elastic force having a low spring constant applies a pre-load to parts of the toothed surfaces of the worm and worm wheel to bring them into contact; and when driven by the electric motor and the worm shaft is moved in the direction going away from the worm wheel by the reaction force applied to the worm shaft from the worm wheel, with the area of meshing moved in the radial direction of the worm shaft with respect to when not driven, the elastic force having a high spring constant applies a pre-load to parts of the toothed surfaces of the worm and worm wheel and brings them into contact.   
     
     
         2 . The assist apparatus for an electric powered power steering apparatus of  claim 1 , wherein the third bearing is a deep-groove type ball bearing having a C2 or C3 internal clearance. 
     
     
         3 . The assist apparatus for an electric-powered power steering apparatus of  claim 1 , wherein the third bearing is a four-point contact type ball bearing. 
     
     
         4 . The assist apparatus for an electric powered power steering apparatus of  claim 1 , wherein the connection between the worm shaft and the rotating shaft is located at a position that coincides in the axial direction with the third bearing. 
     
     
         5 . The assist apparatus for an electric-powered power steering apparatus of  claim 1 , wherein the elastic force is applied to the worm shaft from the elastic-force application means located inside the gear housing without by way of the fourth bearing. 
     
     
         6 . The assist apparatus for an electric-powered power steering apparatus of  claim 1 , wherein the elastic-force application means comprises a torsion coil spring that is located around the worm shaft. 
     
     
         7 . An electric-powered power steering apparatus comprising:
 a steering shaft having a steering wheel located at its rear end;   a pinion that is located at the font end of the steering shaft;   a rack whose teeth mesh with the pinion or a member supported by the pinion, a controller four controlling the drive state of the electric motor; and   an assist apparatus for electric-powered power steering apparatus having a torque sensor, assist shaft, worm wheel, worm shaft, elastic force application means and an electric motor,
 comprising first to fourth bearings, and 
 wherein the torque sensor is located around the steering shaft; the assist shaft is one of the steering shaft, the pinion shaft and a sub-pinion; the worm wheel is fastened around either one of the steering shaft, pinion and sub-pinion; the worm shaft has a worm gear that meshes with the worm wheel; the electric motor comprises a rotating shaft, a rotor that is located on the outer-diameter side of the rotating shaft, and a stator that is located such that it faces the rotor in the radial direction; and the rotating shaft and worm shaft are connected to each other by way of a toothed joint or elastic member, 
 wherein the first bearing supports inside the casing the end section of the rotating shaft on the opposite side from the worm shaft; the second bearing supports inside the casing the portion of the rotating shaft between the joint, which connects the worm shaft and the rotating shaft, and the rotor; the third bearing supports the end of the worm shaft on the side of the rotating shaft inside the gear housing such that the worm shaft can move free tilt, or move in the axial direction, or free tilt and move in the axial direction, within a specified range; and the fourth bearing supports the end of the worm shaft on the opposite side from the rotating shaft inside the gear housing, wherein a clearance in the radial direction is provided between the inner peripheral surface of the inner race of the fourth bearing and the outer peripheral surface of the worm shaft, 
 wherein the elastic-force application means comprises an elastic member having a variable spring constant that can be changed from a low spring constant to a high spring constant, and located between the fourth bearing and the worm shaft so as to apply an elastic force to the worm shaft corresponding to the radial displacement of the worm shaft, wherein when not drivers by the electric motor, the elastic force having a low spring constant applies a pre-load to parts of the toothed surfaces of the worm and worm wheel to bring them into contact; and when driven by the electric motor and the worm shaft is moved in the direction going away from the worm wheel by the reaction force applied to the worm shaft from the worm wheel, with the area of meshing moved in the radial direction of the worm shaft with respect to when not driven, the elastic force having a high spring constant applies a pre-load to parts of the toothed surfaces of the worm and worm wheel and brings them into contact. 
   
     
     
         8 . The electric-powered power steering apparatus of  claim 7 , wherein the third bearing is a deep-groove type ball bearing having a C2 or C3 internal clearance. 
     
     
         9 . The electric-powered power steering apparatus of  claim 7 , wherein the third bearing is a four-point contact type ball bearing. 
     
     
         10 . The electric-powered power steering apparatus of  claim 7 , wherein the connection between the worm shaft and the rotating shaft is located at a position that coincides in the axial direction with the third bearing. 
     
     
         11 . The electric-powered power steering apparatus of  claim 7 , wherein the elastic force is applied to the worm shaft from the elastic-force application means located inside the gear housing without by way of the fourth bearing. 
     
     
         12 . The electric-powered power steering apparatus of  claim 7 , wherein the elastic-force application means comprises a torsion coil spring that is located around the worm shaft.